Sheet feeding device and image forming apparatus

ABSTRACT

One aspect of the present invention provides a sheet feeding device and an image forming apparatus, in which a sheet can stably be separated and fed irrespective of stiffness of the sheet. A movable wall includes a sheet abutting surface that separates the sheet one by one by abutting on the sheet, which is stacked on a tray and fed by a feeding roller. The movable wall is movable in a sheet feeding direction, and a force applying spring applies a force to the movable wall in a direction opposite to the sheet feeding direction. A support portion supports the movable wall such that the movable wall is movable, and such that the movable wall is sloped when abutting on the sheet, which is fed by a feeding roller, and moving on a downstream side in the sheet feeding direction against an applying force of a force applying spring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device and an imageforming apparatus, particularly to a sheet feeding device and an imageforming apparatus, in which a sheet is separated one by one using aseparating slope.

2. Description of the Related Art

Conventionally, an image forming apparatus, such as a copying machine, aprinter, and a facsimile machine, includes a sheet feeding device thatfeeds a sheet to an image forming portion, and a separating portion isprovided in the sheet feeding device in order to separate the sheet oneby one. For example, there is a separating portion including a slopeseparation system (see U.S. Pat. No. 5,622,364). In the slope separationsystem, a separating slope is provided on a leading end side of a trayon which the sheet is stacked, and the sheet fed by a feeding roller ispressed against the separating slope to separate the sheet one by one.

Nowadays, there are various kinds of sheets. Therefore, it is necessaryeven for the conventional sheet feeding device to feed different sheetshaving large or small stiffness. For the conventional sheet feedingdevice including the slope separation system, thick paper having thelarge stiffness is required to be fed by a large conveying force, inorder that the uppermost sheet pressed against the separating slope isconveyed along the separating slope while a leading end of the uppermostsheet is bent upward and separated.

It is conceivable that an angle of the separating slope is decreasedsuch that the uppermost sheet can be conveyed by the small force whileseparated, namely, such that the force necessary to separate and conveythe uppermost sheet is decreased. However, for the decreased angle ofthe separating slope, a force, which presses the uppermost sheet suchthat the next sheet is not fed due to a curvature of the uppermost sheetby the slope, is smaller than a frictional force between the sheets inthe case that thin paper having the small stiffness is fed. In thiscase, a ratio that indicates generation of multi feeding is increasedbecause a lower sheet is conveyed together with the uppermost sheet.That is, separating performance degrades for the sheet having the smallstiffness when the force necessary to separate and convey the sheethaving the large stiffness is decreased, and the force necessary toseparate and convey the sheet having the large stiffness increases whenthe sheet having the small stiffness is securely separated.

It is desirable to provide a sheet feeding device and an image formingapparatus, in which the sheet can stably be separated and fedirrespective of the stiffness of the sheet in the slope separationsystem.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a sheet feeding deviceincludes: a sheet stacking portion on which a sheet is stacked; a sheetfeeding portion which feeds the sheet stacked on the sheet stackingportion; a separating portion which includes a separating slope, theseparating slope separating the sheet one by one by abutting on thesheet fed by the sheet feeding portion, the separating slope beingmovable along a sheet feeding direction; a force applying portion whichapplies a force to the separating portion in a direction opposite to thesheet feeding direction; and a support portion which supports theseparating portion such that the separating portion is movable, and suchthat the separating portion is sloped in connection with the movementwhen abutting on the sheet fed by the sheet feeding portion and moving adownstream side in the sheet feeding direction against an applying forceof the force applying portion.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a configuration of an image formingapparatus including a sheet feeding device according to a firstembodiment of the present invention;

FIG. 2 is a view illustrating a configuration of a separating portionprovided in the sheet feeding device;

FIGS. 3A and 3B are views illustrating movement of a movable wallconstituting the separating portion;

FIGS. 4A and 4B are schematic diagrams illustrating a force applied tothe movable wall;

FIG. 5 is a view illustrating a relationship between an acting force ofa force applying spring, which applies a force to the movable wall, anda conveying force according to a type of sheet;

FIG. 6 is a view illustrating a conveying force of a feeding roller;

FIGS. 7A, 7B, and 7C are views illustrating a sheet feeding operation ofthe sheet feeding device;

FIG. 8 is a view illustrating a relationship between a slope angle ofthe movable wall and the conveying force;

FIG. 9 is a first view illustrating a configuration of a separatingportion provided in a sheet feeding device according to a secondembodiment of the present invention;

FIG. 10 is a second view illustrating the configuration of theseparating portion; and

FIGS. 11A, 11B, and 11C are views illustrating a sheet feeding operationof the sheet feeding device.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings. FIG. 1 is a view illustrating aconfiguration of an image forming apparatus including a sheet feedingdevice according to a first embodiment of the present invention. In FIG.1, the numeral 50 designates a laser beam printer and the numeral 50Adesignates a laser beam printer body (hereinafter referred to as aprinter body). The printer body 50A includes an image forming portion50B. A sheet feeding device 1 that feeds a sheet S, such as a recordingsheet, which is stacked on and stored in a tray 3, to the image formingportion 50B is provided in a lower portion of the printer body 50A.

The image forming portion 50B includes a process cartridge 21, and theprocess cartridge 21 includes a photosensitive drum 21 a, a chargingdevice (not illustrated), a development sleeve (not illustrated), and acleaner (not illustrated). The image forming portion 50B also includes alaser scanner 20 that exposes a surface of the photosensitive drum 21 ato form an electrostatic latent image on the photosensitive drum 21 a.The printer body 50A includes a transfer roller 21 b and a fixingportion 22. The transfer roller 21 b abuts on the photosensitive drum 21a, and constitutes a transfer portion together with the photosensitivedrum 21 a. The fixing portion 22 fixes a toner image, which istransferred by the transfer portion, onto a sheet S.

The sheet feeding device 1 includes a feeding roller 5 and a separatingportion 30. The feeding roller 5 that is of the sheet feeding portionfeeds the sheet S, which is stacked on the tray 3 that is of the sheetstacking portion on which the sheet S is stacked, from the uppermostside. The separating portion 30 separates the sheet one by one. Thefeeding roller 5 is turnably supported by a turning end part of aturning arm 17. The turning arm 17 is supported while being verticallyturnable about a turning shaft 4 that is retained by a stay (notillustrated) fixed to a sheet feeding device body (not illustrated).Irrespective of a stacking level of the sheet S stacked on the tray 3,the feeding roller 5 abuts on an upper surface of an uppermost sheet Saby the turn of the turning arm 17. In the first embodiment, in settingthe sheet S on the tray 3, the sheet S is pushed into the tray 3 from alateral side (a right side of the printer body in FIG. 1) of the printerbody 50A.

An image forming operation of the laser beam printer 50 having the aboveconfiguration will be described below. When the image forming operationis started, the photosensitive drum 21 a rotates clockwise, the surfaceof the photosensitive drum 21 a is charged by the charging device (notillustrated), and the laser scanner 20 emits a laser beam to thephotosensitive drum 21 a based on image information. Therefore, theelectrostatic latent image is formed on the photosensitive drum. Thenthe electrostatic latent image is developed using toner, and visualizedas the toner image.

On the other hand, in parallel with the toner image forming operation,the feeding roller 5 of the sheet feeding device 1 rotates whileabutting on the uppermost sheet Sa on the tray 3, thereby feeding theuppermost sheet Sa. After the uppermost sheet Sa fed by the feedingroller 5 is conveyed by the separating portion 30 while separated one byone, the uppermost sheet Sa is conveyed to the transfer portion by aconveying roller pair 23, and the image on the photosensitive drum 21 ais transferred to the uppermost sheet Sa by the transfer roller 21 b.Then, the uppermost sheet Sa to which the toner image is transferred isconveyed to the fixing portion 22, and unfixed toner image is heated andpressurized by passing between a heating roller 22 a and a pressureroller 22 b, thereby fixing the toner image to the surface of the sheet.A sheet Sa, to which the toner image is already fixed, is discharged ona discharge tray 27 by a discharge roller 26 while the image surface ofthe sheet Sa is oriented downward.

FIG. 2 is a view illustrating a configuration of the separating portion30. Referring to FIG. 2, the separating portion 30 includes a movablewall 6, support members 31 and 32 that movably support the movable wall6, a fixed wall 33, a force applying spring 10 that is of a compressionspring provided between the movable wall 6 and the fixed wall 33, and acam 7. A sheet abutting surface 6 b that is of the separating slope isprovided on the feeding roller side of the movable wall 6. The sheetabutting surface 6 b includes a slope. The sheet S fed by the feedingroller 5 is pressed against the slope, and the slope is inclined withrespect to a vertical direction in which the sheet is conveyed whileseparated one by one. Two bosses (projections) 6 a are projected in eachof side surfaces in a width direction, which is orthogonal to the sheetfeeding direction, of the movable wall 6 that is of the separatingportion movable along the sheet feeding direction. The two bosses 6 aare disposed along the sheet feeding direction in order to determine amoving direction of the movable wall 6 or an attitude of the movablewall 6 during the movement.

First and second boss grooves 9 a and 9 b, in which the bosses 6 a ofthe movable wall 6 are movable, are formed in each of the supportmembers 31 and 32 that are of the support portion movably supporting themovable wall 6. The support members 31 and 32 movably support themovable wall 6 with the first and second boss grooves 9 a and 9 binterposed therebetween. In the first embodiment, the first boss groove9 a located on the side of the sheet abutting surface 6 b of the movablewall 6 is formed in substantially parallel with a sheet stacking surface3 a of the tray 3 in FIG. 1. The second boss groove 9 b located on adownstream side of the boss groove 9 a in the sheet feeding direction isformed sloped such that the downstream side of the second boss groove 9b in the sheet feeding direction is lowered.

As illustrated in FIG. 3A, the movable wall 6 is usually maintained in astandby state in which the bosses 6 a of the movable wall 6 abut onupstream ends of the first and second boss grooves 9 a and 9 b in thesheet feeding direction by the force applying spring 10 provided betweenthe movable wall 6 and the fixed wall 33. The sheet abuts on the movablewall 6 in setting the sheet on the tray, whereby a spring force of theforce applying spring 10 that is of the force applying portion applyingthe force to the movable wall 6 in the direction opposite to the sheetfeeding direction is set to magnitude at which the movable wall 6 doesnot move even if an external force Fx is applied. Therefore, the movablewall 6 is maintained in the standby state in FIG. 3A, when the externalforce Fx is not applied or when the external force Fx is smaller than aforce applying spring acting force Fsp obtained by the applying force ofthe force applying spring 10.

When the external force Fx is larger than the force applying springacting force Fsp of the force applying spring 10, the movable wall 6moves onto the downstream side in the sheet feeding direction while thebosses 6 a move along the first and second boss grooves 9 a and 9 b asillustrated in FIG. 3B. At this point, when the bosses 6 a move, themovable wall 6 is guided by the first and second boss groove 9 a and 9 bdescribed above that is of the guide portion such that the movable wall6 moves onto the downstream side in the sheet feeding direction whilesloped. Therefore, an angle formed between the sheet abutting surface 6b of the movable wall 6 and the sheet stacking surface 3 a of the tray 3changes. The fed sheet moves the movable wall 6 against the applyingforce of the force applying spring 10, and the movable wall 6 moves ontothe downstream side in the sheet feeding direction from the standbyposition in FIG. 3A to the state in FIG. 3B, whereby the angle (a slopeangle) between the sheet abutting surface 6 b and the sheet stackingsurface 3 a changes from θ1 to θ2. That is, the acute angle between thesheet abutting surface 6 b and the sheet stacking surface 3 a decreases(θ1→θ2).

The cam 7 regulates the movement of the movable wall 6 on the downstreamside in the sheet feeding direction, and the cam 7 abuts on the surfaceon the opposite side to the sheet abutting surface 6 b of the movablewall 6 to regulate the movement of the movable wall 6 until the feedingroller 5 starts to feed the sheet. In feeding the sheet, while thefeeding roller 5 rotates, a signal is input to a solenoid (notillustrated) from an electric board (not illustrated) to attract thesolenoid, and a driving force is transmitted from a driving train (notillustrated) to rotate the cam 7. The rotation of the cam 7 that is ofthe regulation portion releases the regulation of the cam 7. Therefore,the movable wall 6 can move onto the downstream side in the sheetfeeding direction when the sheet fed by the feeding roller 5 abuts onthe movable wall 6.

FIG. 4 is a schematic diagram illustrating forces acting onto themovable wall 6, FIG. 4A is a schematic diagram illustrating the forcesacting onto the movable wall 6 in the first embodiment, and FIG. 4B is areference drawing for comparison. In FIG. 4B, a movable wall 206 turnswith a turning center 206 a as a supporting point. The turning center206 a is provided below the sheet stacking surface 3 a. For the movablewall 206, because of a short distance (R2) between the turning center206 a and the sheet abutting surface 206 b of the movable wall 206,force applying spring acting forces Fsp1, Fsp2, and Fsp3 of the forceapplying spring 10 are largely different depending on the position in aheight direction of the sheet abutting surface 206 b.

Therefore, even if external forces Fx1, Fx2, and Fx3 are equal to oneanother, namely, even if forces are equal to one another when the sheetfed by the feeding roller 5 abuts on the movable wall 206, the movablewall 206 easily moves in the case that external force Fx1 acts on theupper side of the sheet abutting surface 6 b. The movable wall 6 hardlymoves in the case that external force Fx3 acts on the lower side of thesheet abutting surface 6 b.

On the other hand, in the case that the bosses 6 a and the first andsecond boss groove 9 a and 9 b guide the movement of the movable wall 6like the first embodiment, the turning center of the movable wall 6 canbe located downward far away from the sheet stacking surface 3 acompared with the case in FIG. 4B. In this case, because of a longdistance (R1) between the turning center and the sheet abutting surface6 b of the movable wall 6, the difference among the force applyingspring acting forces Fsp1, Fsp2, and Fsp3 of the force applying spring10 can be reduced irrespective of the position in the height directionof the sheet abutting surface 6 b. Therefore, a fluctuation in externalforce depending on the position in the height direction of the externalforce (the forces Fx1, Fx2, and Fx3 are equal to one another), which isof a condition that the movable wall 6 moves, namely, the fluctuation inexternal force depending on the stacking level of the sheet S is reducedto stably separate the sheet S.

FIG. 5 is a view illustrating a relationship between the force applyingspring acting force Fsp of the force applying spring 10 and theconveying force of the sheet S according to a type of sheet. In FIG. 5,a vertical axis indicates conveying forces Fz of typical sheet S in asituation in which the movable wall 6 is fixed to the position in thestandby state, namely, the forces, which are generated by the differencein stiffness of the sheet and are necessary to convey the sheet S withthe leading end bent. The vertical axis also indicates a conveying forceFr obtained from the feeding roller 5 and the force applying springacting force Fsp of the force applying spring 10.

The conveying force Fr of the feeding roller 5 will be described withreference to FIG. 6. The conveying force Fr of the feeding roller 5 isobtained by multiplying a normal reaction N, which is generated by therotation and bite of the feeding roller 5, by a friction factor betweenthe feeding roller 5 and the sheet S. The normal reaction N isdetermined by conditions such as a distance h between the turning shaft4 and the uppermost sheet Sa and a distance L between the turning shaft4 and the feeding roller 5. The distance h changes according to thestacking level of the sheet S. The friction factor between the feedingroller 5 and the sheet S is determined by conditions such as a materialfor the feeding roller 5 and the type of the sheet S.

In the first embodiment, the surface of the sheet abutting surface 6 bis set such that the conveying forces Fz for the thin paper (basisweight of 60 g/m²) and the plain paper (basis weight of 80 g/m²) areless than or equal to about 3 N, and such that the conveying forces Fzfor the thick paper (basis weight of 160 g/m²) and an envelope aregreater than or equal to about 10 N. At this point, the conveying forceFr obtained from the feeding roller 5 is substantially kept constanteven if the distance h changes. In setting the conveying force Fr to agiven value, the force applying spring acting force Fsp of the forceapplying spring 10 is set so as to be greater than the conveying forcesFz for the plain paper and the thin paper and so as to be less than theconveying forces Fz for the thick paper and the envelope and theconveying force Fr of the feeding roller 5. Therefore, in the firstembodiment, the force applying spring acting force Fsp of the forceapplying spring 10 is set to 5 N in order to satisfy the aboveconditions.

A sheet feeding operation of the sheet feeding device 1 will bedescribed below with reference to FIG. 7. FIG. 7A illustrates the statewhen a user sets the sheet S into the tray 3. At this point, the cam 7is located at a home position to abut on the surface on the oppositeside to the sheet abutting surface 6 b of the movable wall 6, wherebythe movement of the movable wall 6 is regulated. When the user sets thesheet S into the tray 3, the movable wall 6 does not move even if thesheet S abuts on the movable wall 6. Therefore, the user can easily setthe sheet S by abutting the leading end of the sheet S on the movablewall 6. That is, a good setting property can be provided in setting thesheet S.

FIG. 7B illustrates the state in which the thin paper having the basisweight of 60 g/m² is fed. In the case that the sheet is fed, the signalis input to the solenoid from the electric board (not illustrated) tostart the rotation of the cam 7, the cam 7 separates from surface on theopposite side to the sheet abutting surface 6 b of the movable wall 6,and the movable wall 6 is put into the movable state.

When the feeding roller 5 starts the rotation to feed the uppermostsheet Sa abutting on the feeding roller 5, the uppermost sheet Sa ispressed against the sheet abutting surface 6 b of the movable wall 6 towhich the applying force is applied by the force applying spring 10. Atthis point, although the conveying force Fr of the feeding roller 5 isapplied to the movable wall 6, the conveying force Fr necessary toconvey the uppermost sheet Sa with the leading end bent is smaller thanthe force applying spring acting force Fsp of the force applying spring10 because the uppermost sheet Sa is the thin paper. Therefore, themovable wall 6 does not move.

When the uppermost sheet Sa is further pressed against the sheetabutting surface 6 b of the movable wall 6 while the movable wall 6 doesnot move, the uppermost sheet Sa is fed while only the leading end ofthe uppermost sheet Sa is bent. Therefore, the uppermost sheet Saseparates from the lower sheet, and the uppermost sheet Sa is conveyedto the conveying roller pair 23 while guided by the sheet abuttingsurface 6 b of the movable wall 6.

At this point, in the lower sheet, the conveying force Fr of the feedingroller 5 is insufficient because the conveying force Fr acts on thelower sheet via the frictional force between the sheets. Even if theleading end of the lower sheet abuts on the sheet abutting surface 6 bof the movable wall 6, the leading end is not bent and the lower sheetis not conveyed. Therefore, the lower sheet is not fed together with theuppermost sheet Sa, and the multi feeding is not generated. After theuppermost sheet Sa is conveyed to the conveying roller pair 23, the cam7 again reaches the home position at which the cam 7 abuts on thesurface on the opposite side to the sheet abutting surface 6 b of themovable wall 6, and the cam 7 stops the rotation.

FIG. 7C illustrates the state in which the thick paper having the basisweight of 160 g/m² is fed. In this case, the uppermost sheet Sa isconveyed by the rotation of the feeding roller 5, and pressed againstthe sheet abutting surface 6 b of the movable wall 6 to which the forceis applied by the force applying spring 10. At this point, although theconveying force Fr of the feeding roller 5 is applied to the movablewall 6, the conveying force Fr has predetermined stiffness or morebecause the sheet is the thick paper. Therefore, the conveying force Fris larger than the force applying spring acting force Fsp of the forceapplying spring 10, which is necessary to convey the uppermost sheet Sawith the leading end bent.

Accordingly, the uppermost sheet Sa presses the movable wall 6 withoutbending the leading end, and the movable wall 6 moves along the firstand second boss grooves 9 a and 9 b. The movement of the movable wall 6decreases the slope angle θ formed between the sheet abutting surface 6b and the sheet stacking surface 3 a.

FIG. 8 illustrates a relationship between the conveying force Fz and theslope angle θ in feeding the thick paper having the basis weight of 160g/m². As can be seen from FIG. 8, the conveying force Fz necessary toconvey the sheet S with the leading end bent decreases with decreasingslope angle θ. In FIG. 8, when the slope angle Γ reaches about 72°, themovement of the movable wall 6 is stopped by the applying force of theforce applying spring 10 to bend the leading end of the uppermost sheetSa. Then, the uppermost sheet Sa is conveyed to the conveying rollerpair 23 while guided by the sheet abutting surface 6 b and the guide.

At this point, in the lower sheet, the conveying force Fr of the feedingroller 5 is insufficient because the conveying force Fr acts on thelower sheet via the frictional force between the sheets, but the leadingend of the lower sheet cannot be bent and conveyed even if the leadingend of the lower sheet abuts on the sheet abutting surface 6 b.Therefore, the lower sheet is not fed together with the uppermost sheetSa, and the multi feeding is not generated. After the uppermost sheet Sais conveyed to the conveying roller pair 23, the cam 7 again reaches thehome position at which the cam 7 abuts on the surface on the oppositeside to the sheet abutting surface 6 b of the movable wall 6, and thecam 7 stops the rotation.

As described above, in the first embodiment, the movable wall 6 ismovably provided, and the movable wall 6 is sloped by the movement.Therefore, a wide variety of sheets from the thin paper that is of thesheet having weak conveying force to the thick paper or envelope that isof the sheet having the strong conveying force can surely be separatedand fed. The turning center of the movable wall 6 is largely separatedbelow the sheet stacking surface 3 a, so that the change in forceapplying spring acting force Fsp of the force applying spring 10 actingon the uppermost sheet Sa can be decreased even if the stacking level ofthe sheet S changes. As a result, the fluctuation of the condition thatthe movable wall 6 moves according to the stacking level of the sheet Scan be decreased and the stable sheet separating and feeding performancecan be exerted.

In the first embodiment, the movable wall 6 having the sheet abuttingsurface 6 b is sloped when the sheet fed by the feeding roller 5 abutson the movable wall 6 to move the movable wall 6. Therefore, the sheetcan stably be separated and fed irrespective of the stiffness of thesheet.

As described above, in the first embodiment, the good setting propertycan be provided by providing the cam 7 when the user sets the sheet intothe tray. The stable sheet separating and feeding performance can alsobe exerted even in the case that the cam 7 is not provided.

A second embodiment of the present invention will be described below.FIGS. 9 and 10 are views illustrating a configuration of a sheet feedingdevice according to a second embodiment. In FIGS. 9 and 10, thecomponent identical or equivalent to that in FIGS. 2 and 3 is designatedby the identical numeral.

In the second embodiment, as illustrated in FIGS. 9 and 10, the firstboss groove 9 a is formed so as to be inclined obliquely upward withincreasing distance from the feeding roller 5. In the case that thefirst boss groove 9 a in FIGS. 9 and 10 is formed, the angle formedbetween the sheet abutting surface 6 b of the movable wall 6 and thesheet stacking surface 3 a changes when the movable wall 6 moves, andthe upper end of the sheet abutting surface 6 b is always higher than aheight H6 at the position in the standby state irrespective of amovement amount of the movable wall 6.

FIG. 11A illustrates the state in which the user sets the sheet S intothe tray 3 in the second embodiment. At this point, the cam 7 abuts onthe surface on the opposite side to the sheet abutting surface 6 b ofthe movable wall 6. FIG. 11B illustrates the state in which the thinpaper having the basis weight of 60 g/m² is fed. At this point, the cam7 separates from the movable wall 6, and the movable wall 6 is in themovable state.

When the feeding roller 5 starts the rotation to feed the uppermostsheet Sa, the uppermost sheet Sa is pressed against the sheet abuttingsurface 6 b of the movable wall 6 to which the applying force is appliedby the force applying spring 10. At this point, the movable wall 6 is inthe movable state, and the conveying force Fr of the feeding roller 5 isapplied to the movable wall 6 via the uppermost sheet Sa. However, theconveying force Fr necessary to convey the sheet S with the leading endbent is smaller than the force applying spring acting force Fsp of theforce applying spring 10 because the uppermost sheet Sa is the thinpaper. Therefore, the movable wall 6 does not move.

When the uppermost sheet Sa is further pressed against the sheetabutting surface 6 b of the movable wall 6 while the movable wall 6 doesnot move, the uppermost sheet Sa is fed while only the leading end ofthe uppermost sheet Sa is bent, thereby separating the uppermost sheetSa from the lower sheet. The separated uppermost sheet Sa is conveyed tothe conveying roller pair 23 while guided by the sheet abutting surface6 b of the movable wall 6.

At this point, in the lower sheet, the conveying force Fr of the feedingroller 5 is small because the conveying force Fr acts on the lower sheetvia the frictional force between the sheets. Even if the leading end ofthe lower sheet abuts on the sheet abutting surface 6 b of the movablewall 6, the leading end is not bent and the lower sheet is not conveyed.Therefore, the lower sheet is not fed together with the uppermost sheetSa, and the multi feeding is not generated. After the uppermost sheet Sais conveyed to the conveying roller pair 23, the cam 7 again reaches thehome position at which the cam 7 abuts on the surface on the oppositeside to the sheet abutting surface 6 b of the movable wall 6, and thecam 7 stops the rotation.

FIG. 11C illustrates the state in which the thick paper having the basisweight of 160 g/m² is fed. At this point, the cam 7 separates from themovable wall 6, and the movable wall 6 is in the movable state. When thefeeding roller 5 starts the rotation to feed the uppermost sheet Sa, theuppermost sheet Sa is pressed against the sheet abutting surface 6 b ofthe movable wall 6 to which the force is applied by the force applyingspring 10. At this point, the movable wall 6 is in the movable state,and the conveying force Fr of the feeding roller 5 is applied to themovable wall 6. However, the conveying force Fr necessary to convey theuppermost sheet Sa with the leading end bent is larger than the forceapplying spring acting force Fsp of the force applying spring 10 becausethe uppermost sheet Sa is the thick paper. Therefore, the movable wall 6moves along the first and second boss grooves 9 a and 9 b.

When the movable wall 6 moves, the slope angle θ formed between thesheet abutting surface 6 b and the sheet stacking surface 3 a changesaccording to the movement amount. The relationship between the slopeangle θ and the conveying force Fz for the thick paper having the basisweight of about 160 g/m² is illustrated in FIG. 8 described above, andthe second embodiment conforms to the relationship in FIG. 8. Referringto FIG. 8, the leading end of the uppermost sheet Sa is bent when theslope angle θ reaches about 72°, and then the uppermost sheet Sa isconveyed to the conveying roller pair 23 while guided by the sheetabutting surface 6 b and a guide on the downstream side.

At this point, in the lower sheet, the conveying force Fr of the feedingroller 5 is small because the conveying force Fr acts on the lower sheetvia the frictional force between the sheets, but the leading end of thelower sheet cannot be bent and conveyed even if the leading end of thelower sheet abuts on the sheet abutting surface 6 b. Therefore, thelower sheet is not fed together with the uppermost sheet Sa, and themulti feeding is not generated. After the uppermost sheet Sa is conveyedto the conveying roller pair 23, the cam 7 again reaches the homeposition at which the cam 7 abuts on the surface on the opposite side tothe sheet abutting surface 6 b of the movable wall 6, and the cam 7stops the rotation.

In the case that the first boss groove 9 a is formed in substantiallyparallel to the sheet stacking surface 3 a, when the movable wall 6 issloped by the movement, the level at the upper end of the sheet abuttingsurface 6 b of the movable wall 6 is lowered compared with the height H6at the position in the standby state as the movable wall 6 moves asillustrated in FIG. 7. On the other hand, in the second embodiment, thefirst boss groove 9 a is formed so as to be inclined obliquely upwardwith increasing distance from the feeding roller 5. In the secondembodiment, when the movable wall 6 is sloped by the movement, the levelat the upper end of the sheet abutting surface 6 b of the movable wall 6is not lower than the height H6 at the position in the pre-slope standbystate.

Therefore, the leading end of the uppermost sheet Sa can surely beguided to a given level by the sheet abutting surface 6 b of the movablewall 6 irrespective of the movement amount of the movable wall 6, andthe sheet can be fed without generating a conveying failure in a gapwith the guide on the downstream side or a step.

As described above, in the second embodiment, the first boss groove 9 ais formed so as to be inclined obliquely upward with increasing distancefrom the feeding roller 5. Therefore, while the performance of stablyseparating and feeding the sheet with the sheet pressed against thesheet abutting surface 6 b of the movable wall 6 is maintained, thesheet can surely be fed even if the movable wall 6 moves.

In the configuration of the second embodiment, the upper end of thesheet abutting surface 6 b is always the height H6 at the position inthe standby state irrespective of a movement amount of the movable wall6. However, the second embodiment is not limited to this, and dependingon a shape of the boss groove 9 a, the upper end of the sheet abuttingsurface 6 b may be higher than the height H6 at the position in thestandby state as the movable wall 6 moves. Even in this case, theleading end of the uppermost sheet Sa can surely be guided to the givenlevel or more by the sheet abutting surface 6 b of the movable wall 6even if the movable wall 6 moves.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2012-263766, filed Nov. 30, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A sheet feeding device comprising: a sheetstacking portion on which a sheet is stacked; a sheet feeding portionwhich feeds the sheet stacked on the sheet stacking portion; aseparating portion which includes a separating slope, the separatingslope separating the sheet one by one by abutting on the sheet fed bythe sheet feeding portion, the separating portion being movable along asheet feeding direction; a force applying portion which applies a forceto the separating portion in a direction opposite to the sheet feedingdirection; and a support portion which supports the separating portionsuch that the separating portion is movable, and such that theseparating portion is sloped in connection with the movement whenabutting on the sheet, which is fed by the sheet feeding portion, andmoving on a downstream side in the sheet feeding direction against anapplying force of the force applying portion.
 2. The sheet feedingdevice according to claim 1, wherein the support portion includes aguide portion which guides the separating portion when the separatingportion moves onto the downstream side in the sheet feeding directionwhile sloped.
 3. The sheet feeding device according to claim 2, whereinthe guide portion is formed such that an upper end position of theseparating slope is higher than a level of the pre-slope upper endposition when the separating portion is sloped.
 4. The sheet feedingdevice according to claim 1, wherein the applying force of the forceapplying portion is set to magnitude at which the separating portionmoves when the sheet having predetermined stiffness or more abuts on theseparating portion.
 5. The sheet feeding device according to claim 1,wherein the support portion includes a projection and a groove, theprojection guiding the separating portion when the separating portionmoves onto the downstream side in the sheet feeding direction whilesloped, the projection being guided in the groove, a pair of theprojection and the groove is disposed on each of both sides of theseparating portion along the sheet feeding direction, and when theseparating portion moves on the downstream side in the sheet feedingdirection, the groove disposed on an upstream side substantiallyhorizontally or upwardly guides the projection and the groove disposedon the downstream side downwardly guides the projection.
 6. The sheetfeeding device according to claim 1, further comprising a regulationportion which abuts on the separating portion to regulate the movementof the separating portion on the downstream side in the sheet feedingdirection until the sheet feeding portion starts to feed the sheet. 7.An image forming apparatus comprising: a sheet feeding device including:a sheet stacking portion on which a sheet is stacked; a sheet feedingportion which feeds the sheet stacked on the sheet stacking portion; aseparating portion which includes a separating slope, the separatingslope separating the sheet one by one by abutting on the sheet fed bythe sheet feeding portion, the separating portion being movable along asheet feeding direction; a force applying portion which applies a forceto the separating portion in a direction opposite to the sheet feedingdirection; and a support portion which supports the separating portionsuch that the separating portion is movable, and such that theseparating portion is sloped in connection with the movement whenabutting on the sheet, which is fed by the sheet feeding portion, andmoving on a downstream side in the sheet feeding direction against theapplying force of the force applying portion, and an image formingportion which forms an image on the sheet fed from the sheet feedingdevice.
 8. The image forming apparatus according to claim 7, wherein thesupport portion includes a guide portion which guides the separatingportion when the separating portion moves onto the downstream side inthe sheet feeding direction while sloped.
 9. The image forming apparatusaccording to claim 8, wherein the guide portion is formed such that anupper end position of the separating slope is higher than a level of thepre-slope upper end position when the separating portion is sloped. 10.The image forming apparatus according to claim 7, wherein the applyingforce of the force applying portion is set to magnitude at which theseparating portion moves when the sheet having predetermined stiffnessor more abuts on the separating portion.
 11. The image forming apparatusaccording to claim 7, wherein the support portion includes a projectionand a groove, the projection guiding the separating portion when theseparating portion moves onto the downstream side in the sheet feedingdirection while sloped, the projection being guided in the groove, apair of the projection and the groove is disposed on each of both sidesof the separating portion along the sheet feeding direction, and whenthe separating portion moves on the downstream side in the sheet feedingdirection, the groove disposed on an upstream side substantiallyhorizontally or upwardly guides the projection and the groove disposedon the downstream side downwardly guides the projection.
 12. The imageforming apparatus according to claim 7, further comprising a regulationportion which abuts on the separating portion to regulate the movementof the separating portion on the downstream side in the sheet feedingdirection until the sheet feeding portion starts to feed the sheet.